Why it matters
The form is the starting point for the capital gain or loss on each sale. A missing basis or a sale the broker did not report can change the tax, and the taxpayer needs the trade confirmations to fill the gap.
Example
A client sells shares through a broker. The broker sends Form 1099-B with the proceeds and the basis, and the preparer reports the gain or loss on the return.
Related terms
Questions about Form 1099-B
Does Form 1099-B report every sale?
It reports the sales the broker is required to report. Some transactions, such as certain private sales or barter exchanges, may not appear on a 1099-B, so the client should keep the trade records.
What if the cost basis is missing?
The client needs the purchase records or the broker's supplemental statement. Without the basis, the preparer may have to treat the basis as zero, which overstates the gain.